Switching noise at operation frequency of an electronic device and the like as well as its harmonic frequency might be mixed in output voltage and an output signal output from a switching power supply and other electronic devices via a conducting bar. Such switching noise might negatively affect supplying devices such as an external electronic device, and thus needs to be reduced as appropriate. The switching power supply outputs output voltage of a predetermined voltage value through a switching operation of a power transistor. When the power transistor is turned ON and OFF, the current path is switched, and this might generate noise at a switching frequency and its harmonic frequency depending on a rated output. The noise is superimposed on the output voltage to be transmitted to the supplying device via the conducting bar and negatively affects the supplying device. Thus, a device for reducing such noise needs to be provided. In one known output-noise reduction device, a conducting bar is inserted to a magnetic body core to form a noise filter for removing the noise flowing in the conducting bar (see, for example, Patent Literature 1).
[Patent Literature 1] Japanese Laid-open Patent Publication No. 2005-93536